1. Field of the Invention
The present invention relates to testing apparatus and more particularly to an improved apparatus for the accelerated testing of the corrosion resistance of a plurality of parts under exacting repetitive conditions.
2. Description of the Art
The industry of precision powder metallurgical parts, including structural components, and plated parts has experienced significant growth over the past decade. As a result of such growth especially into areas where the use of such parts is critical, quality control of the manufacturing process has become increasingly important.
An exemplary quality control application for such parts is the testing of corrosion resistance. Testing a part for corrosion resistance in its actual operating environment is too time consuming to provide the rapid feedback necessary to effectively control quality.
It has been found that corrosion resistance may be determined relatively quickly by an accelerated test involving repetitive immersion of a part in a corrosive liquid following intermittent drying of the part. A known apparatus which may be used for repetitively immersing a part in liquid corrosive media is a rotary Ferris wheel type design in which the parts to be tested are placed in individual baskets located around the periphery of the wheel. The wheel is located over a corrosive bath such that the part is immersed in the corrosive media as each basket passes through its lower area of rotation. The part comes out of the bath as the basket is moved upwardly upon continued rotation of the wheel. Shortcomings of this type of apparatus include the necessity of constructing a reservoir with sufficient size to accommodate the rotary path of the baskets. Also, the time of immersion is necessarily related to the drying time as both are functions of the depth of the bath and the wheel speed. For example, increasing the time of immersion, by reducing the speed of the wheel, causes a corresponding increase in the drying time. Likewise, increasing the wheel speed to decrease the time of immersion of a part results in a decrease in the drying time. Further, the same reservoir of corrosive liquid must necessarily be used for all parts in the test, while it is often desirable to test the similar parts from the same stock in a plurality of corrosive liquids. Also, with a wheel type design corrosives may drip from one part, or basket, to another part located therebelow sometimes affecting the test results.
The American Society for Testing Materials (ASTM) has published specifications for detecting the susceptibility to intergranular attack in molybdenum bearing stainless steels, see ASTM Test No. A262, Practice D. The apparatus described for conducting such test includes polyvinyl chloride cylinders, specimen holders and a constant temperature acidic bath. The prepared specimens are supported in the cylinder and the cylinder is filled with acid solution and heated. After adequate exposure to the solution the specimens are removed.
A variety of other test apparatus are known in the art which include baskets in which a plurality of parts are stacked for simultaneous immersion into a corrosive bath. Such apparatus require immersion of all of the parts into the same bath. A drawback of this system is that if the common bath becomes contaminated, the entire test procedure may have to be repeated. Also such apparatus may exhibit drainage problems when the residual bath on the upper or adjacent stacked parts drains over the lower or adjacent stacked parts as the basket is removed for drying of the parts.
An apparatus for simultaneously raising and lowering a plurality of parts into liquid corrosive media is also known in which the parts are repeatedly immersed and dried. Drying in such apparatus is accomplished by a plurality of heat lamps located adjacent the apparatus. In addition to the heat lamps being separate from the unit, such apparatus has separate power controls which, when installed, limit the portability thereof. Further, the apparatus does not include an isolated environment in which the repetitive test procedure is isolated from the ambient atmosphere. Furthermore, heat lamps do not provide a temperature in a heating or drying zone that can be tightly controlled to yield extremely accurate and comparative test results as may be required in certain corrosion test applications. Also, such apparatus does not enhance unobstructed visual inspection of the parts at any stage of the repetitive test.
For corrosion resistance tests to yield accurate measurements which are valuable for comparison purposes all test criteria, including immersion time, drying time, drying temperature, and isolation from the ambient environment must be maintained and controlled within tight tolerances. For example, no technician can accurately position a test sample on a repetitive manual basis with any degree of consistency. Manual testing tends to yield inaccurate results because of the inability to repeat dipping of a test sample at the same angle, depth or time with each repetitive cycle. The same inaccuracies are found in various, prior art drying devices. The necessity for control is especially true when considering that adequate accelerated corrosion tests require relatively long test periods on the order of eight hours. It is important to repeat the steps of the accelerated corrosion test under as exact repetitive conditions as is possible in order to obtain meaningful comparative data.
Accordingly an accelerated corrosion test apparatus is desired which is able to determine the corrosion resistance of a plurality of parts by testing such parts in a controlled environment to yield more accurate results than test apparatus known heretofore. Ideally, such apparatus shall provide the industry with a unit which is able to control corrosion test parameters sufficient to establish a commercially acceptable standard corrosion testing apparatus.